As any part of your procedure, did you actually do a Library Restore inside JRiver? You refer to "importing" but that means something different.
If you have enabled auto-import to run in the background, that can complicate things while you are trying to fix this. Don't allow auto-import to run, automatically or manually, until you have fixed your situation.
I think, but am not 100% sure (not going to try it on my own library) that if files are auto-deleted from the library due to broken links, their entries in playlists are also deleted. In which case, the only way to get them back is a library restore.
There have been good tutorials (written by Roderick, I believe) about moving files in similar situations. Very briefly, what it sounds like would correct your situation is this:
1. Library restore of a good library (select both Library and Settings when restoring)
2. Turn off auto import
3. Since Auto-import might have run while you were messing about, restore the same library again, but select ONLY "Restore library and playlists" and do NOT check "Restore settings". This will again repopulate your library and playlists, albeit with broken links.
4. Use Rename, Move and Copy files, selecting the "Update database..." option, and fix the paths to your broken files.
See this link for more info:
https://wiki.jriver.com/index.php/Rename,_Move,_and_Copy_Files5. Verify your links are now good, before re-enabling auto import.
You can check for broken links by creating a smartlist called "Broken Links" with the following as a rule of type Custom:
[=ismissing([filename])]=1
Let us know if you can see daylight from that hole you're in.